simple two speed belt or chain drive idea

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mechhead
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simple two speed belt or chain drive idea

Post by mechhead » Apr 15, 2018 8:52 pm

Here is the outline of a two speed belt or chain drive idea that is very simple with only two belts or chains between the motor and wheel. The idea is similar to the two speed belt drive on the evo/uber petrol scooter, and similar to Thud's two speed box.

first gear:
motor drives through both belt/chains motor rpm is reduced around 2:1 in the first belt/chain that is very short with further reduction through the final drive belt/chain, ratio dependent on what you want for the final reduction, wheel size and speed requirements.

second gear: drive is through the final drive belt/chain only, with only one stage of reduction.

parts arrangement:

device comprised of motor shaft, jackshaft and two belts/chains, the final drive belt/chain path wraps the rear wheel sprocket, jack shaft sprocket ~180 degree wrap, tensioner 180 degree wrap, motor shaft sprocket ~180deg wrap then back to the rear wheel.

shifting: there are a number of options here, a single clutch (friction or dog) on the motor shaft to final drive belt/chain sprocket and a freewheel/ one way bearing on the first gear jackshaft to final drive sprocket this allows the motor to freewheel in first gear but be locked for regen in second.

second option is a double dog clutch on the motor shaft where loading is lowest with a neutral position allowing disenguagement or regen in both gears this is my preferred arrangement.

This design allows the first gear chain/belt and dog clutch mechanism to be encased and allow good lubrication of clutches and first gear chain if used and only two belts /chains to be used, with only the final drive in the open with dirt and crud, the use of a belt here is probably preferable as it is likely to be on the left side with the rear disk brake but i would bet that with two gears and regen the back brake is never used unless something fails.

If I build this it will be likely all built on to a lengthened swing arm using an unshelled BPM 6t motor I have already (50kv 1500w cont ), but there are plenty of suitable motors for this type of setup.

Let me know what you think people.

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Chalo
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Re: simple two speed belt or chain drive idea

Post by Chalo » Apr 15, 2018 10:51 pm

If you're going to employ some kind of clutch, why the elaborate tension/jackshaft/idler system? You could just have two parallel single speeds, with the higher ratio clutched and the lower one freewheeling on overrun.

Check out this cool historical two-speed gearing system-- one ratio when pedaled forward, the other when pedaled backwards:
https://en.m.wikipedia.org/wiki/Retro-direct
Image
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mechhead
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Re: simple two speed belt or chain drive idea

Post by mechhead » Apr 15, 2018 11:46 pm

thanks Chalo,
I'm familiar with the retro direct system and reversing motor dual speeds like the xiongda hub having read all the threads about two speed drives i can find, the reason I like the dual clutch design with one very short belt and two driving sprokets on the final drive is, it allows motor disconnect and regen in both gears, with the dual final drive set up with over run freewheel on the low speed you only get regen in high gear. I'm trying to work out the simplest way to have both regen and freewheel in both gears. The dual final drive has its attractions but fitting two belts side by side on the left of the rear wheel could be challenging but with a chain not so difficult as they are much narrower for a given power capacity and the sprokets are cheaper and more available, chains do have their attractions.

The retro direct idea has its own merits and needs no clutch but also does not enable regen at all for me the set up would be for cargo hauling up hilly roads and would yield good returns with regen because of the weight and low speeds most of the time and the need to constantly replace brake pads if there is no regen option. Perhaps a brake only friction clutch on the first gear in a retro direct combination could give the simplest implementation of regen and 2 speeds

The single clutch on the high gear has its attractions as well as it allows one less clutch and the use of an over run freewheel on first gear.

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Chalo
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Re: simple two speed belt or chain drive idea

Post by Chalo » Apr 16, 2018 12:19 am

Regen is apt to tear up whatever chain tensioner you put on a single chain system. It takes a lot of structural integrity in both the idler pulley and its mount if you have an idler on the load carrying side of the chain, such as would be necessary for regen.
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mechhead
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Re: simple two speed belt or chain drive idea

Post by mechhead » Apr 16, 2018 12:32 am

Chalo,
I think you have me sold on the retro direct reversing motor system as my controller is capable of that, being a vesc-x ( new name foc-box ) and its far easier to build with two freewheels on the motor shaft, one with a friction clutch incorporated for regen on the first gear that should give excellent regen braking.

Much simpler than my initial idea, and it allows the motor to go dead when rolling unless the regen clutch is used, and it can be done with just one bmx chain, the motor I have is a gutted 6t BPM geared hub, a nice axially thin large diameter outrunner of about 50kv that should with a heat sink on the stator end turns be good for a couple of kw and more for burst, my controller is capable of 12s 80a with adequate cooling. I was initially going to build a crossbreak style mid drive out of the BPM but after seeing how the bbshd I worked on recently ate sprockets and chains in such quick time I'm reluctant to push that kind of power through HG chain even on an 8 speed and bmx chain on standard bicycle sprockets looks like a much better alternative. The only bit of custom machining required is the friction clutch and the idler can be sprung with an elastomer to reduce shock loading nicely, just one custom swing arm to fabricate... cant be too hard with a welder and some rectangular cromo tube.

In a retro direct system the tensioner is under the full load in one of the gears so would need to be strong.

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Alan B
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Re: simple two speed belt or chain drive idea

Post by Alan B » Apr 16, 2018 12:37 am

Best to use a design that doesn't need tensioners (on the tensioned side), putting a tensioner on that side of a belt/chain never seems to work out.

Normally the retro-direct designs lockup when rolling backwards, this is often a problem. Perhaps your half-friction clutch will fix that, of course then it is not exactly a retro-direct.

mechhead
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Re: simple two speed belt or chain drive idea

Post by mechhead » Apr 16, 2018 12:57 am

Ok back to system one or a system with one freewheel and one clutch or two clutches , reversing with cargo is often necessary, that would realy suck and I never liked powered idlers and the missaligned chain of a retrodirect .

The evo scooter belt box is kind of nice, they are cheap but apparently don't last very long. with their nylon tensioners and unsealed bearing inside the clutch roller but the clutch bits and shaft are rather nice and the unsealed bearing can be replaced with a proper one maby many of the parts in one of these could be recycled in to the finished version, as im trying to com eup with a design that uses only off the shelf wearing parts so its easy to maintain and build.

http://scooter.wikia.com/wiki/Evo_two_s ... ansmission

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